The proposed research deals with the molecular properties of brain microtubules including: tubulin-nucleotide interactions; fluorescence studies of microtubule assembly; related enzymology of several nucleotide-dependent enzymes associated with microtubules; rates of tubulin depolymerization; and identification and characterization of microtubule associated proteins. Each area of interest draws in part upon past expertise with other phosphotransfer enzymes, covalent modification of proteins, and enzyme kinetics. The basic rationale is to combine a balanced attack using chemical, physical and kinetic probes to learn more about the fundamental properties of microtubules. The work is an outgrowth of an ongoing research project on microtubule assembly and interactions, and the proposed experiments are based upon a broad base of experience developed over the past three years with microtubule systems.